Manipulation of ferromagnets via the spin-selective optical Stark effect

Qaiumzadeh, Alireza; Bauer, G.; Brataas, Arne

doi:10.1103/physrevb.88.064416

Cited by 27 publications

(25 citation statements)

References 42 publications

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“…The IFE is an optomagnetic counterpart of the magneto-optical Faraday effect, that is, the circularly polarized laser light imparts a magnetization in the material which exerts a torque on the pre-existing magnetization and assists the magnetization switching. However, although various models for the IFE have been proposed [11][12][13][14][15][16][17] there does as yet not exist any knowledge as to how the induced magnetization, or optomagnetic field arises, and even less is known about the materials dependence of the IFE. As materials specific theory is lacking it is neither known for which materials large effects are predicted nor how the IFE could be optimized to trigger reversal with minimal laser power.…”

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confidence: 99%

Ab InitioTheory of Coherent Laser-Induced Magnetization in Metals

et al. 2016

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We present the first materials specific ab initio theory of the magnetization induced by circularly polarized laser light in metals. Our calculations are based on non-linear density matrix theory and include the effect of absorption. We show that the induced magnetization, commonly referred to as inverse Faraday effect, is strongly materials and frequency dependent, and demonstrate the existence of both spin and orbital induced magnetizations which exhibit a surprisingly different behavior. We show that for nonmagnetic metals (as Cu, Au, Pd, Pt) and antiferromagnetic metals the induced magnetization is antisymmetric in the light's helicity, whereas for ferromagnetic metals (Fe, Co, Ni, FePt) the imparted magnetization is only asymmetric in the helicity. We compute effective optomagnetic fields that correspond to the induced magnetizations and provide guidelines for achieving all-optical helicity-dependent switching.PACS numbers: 78.20. Ls, 75.70.Tj, 75.60.Jk All-optical helicity-dependent magnetization switching has recently emerged as a promising way to manipulate and ultimately control the magnetization in a magnetic material using ultrashort optical laser pulses [1][2][3][4][5][6][7]. As femtosecond optical laser pulses are the shortest stimuli known to mankind, all-optical helicity-dependent switching offers novel options to achieve magnetization reversal at a hitherto unprecedented speed. The action of a circularly polarized laser pulse on the magnetization of a material was at first observed for an antiferromagnetic 3d-metal oxide [1] and later magnetization reversal was demonstrated in a ferrimagnetic rare-earth transitionmetal alloy [2,8]. Importantly, recent work demonstrated that all-optical helicity-dependent switching is not limited to a special class of materials, but can be achieved in a broader variety of material classes, including metallic multilayers, synthetic ferrimagnets [6], and even ferromagnets such as FePt [7], which is the prime candidate material for future ultradense magnetic recording [9].While these discoveries exemplify that ultrafast magnetization reversal driven by circularly polarized laser pulses could soon revolutionize magnetic recording its underlying physical mechanism is poorly understood. The influence of the circularly polarized laser pulse has been attributed to the inverse Faraday effect (IFE) [1][2][3]7], which was discovered fifty years ago [10]. The IFE is an optomagnetic counterpart of the magneto-optical Faraday effect, that is, the circularly polarized laser light imparts a magnetization in the material which exerts a torque on the pre-existing magnetization and assists the magnetization switching. However, although various models for the IFE have been proposed [11][12][13][14][15][16][17] there does as yet not exist any knowledge as to how the induced magnetization, or optomagnetic field arises, and even less is known about the materials dependence of the IFE. As materials specific theory is lacking it is neither known for which materials large effects are pr...

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Ab InitioTheory of Coherent Laser-Induced Magnetization in Metals

et al. 2016

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“…Here, the current-induced spin polarization would induce torques on the magnetic order parameter, eventually causing magnetization switching. The spin-dependent dynamic Stark effect also induces torques by circularly polarized light [14]. The two processes are independent and should be added.…”

Section: Discussionmentioning

confidence: 99%

“…This is in contrast to the IFE phenomenology. Recently, strong effective magnetic fields were calculated for magnetic semiconductors that are caused by the spin-selective dynamical Stark effect [14].…”

Section: Introductionmentioning

confidence: 99%

Light-induced spin polarizations in quantum rings

2014

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Nonresonant circularly polarized electromagnetic radiation can exert torques on magnetizations by the inverse Faraday effect (IFE). Here, we discuss the enhancement of IFE by spin-orbit interactions. We illustrate the principle by studying a simple generic model system, i.e., the quasi-one-dimensional ring in the presence of linear/cubic Rashba and Dresselhaus interactions. We combine the classical IFE in electron plasmas that is known to cause persistent currents in the plane perpendicular to the direction of the propagation of light with the concept of current and spin-orbit-induced spin transfer torques. We calculate light-induced spin polarization that in ferromagnets might give rise to magnetization switching.

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“…Laser heating was thus suspected to have been assisting the switching2 but this assumption was not supported by subsequent experiments12. Now the switching has been basically regarded as an all-optical effect3 but a consensus description has not yet been reached despite many theoretical efforts have been devoted to it131415161718192021. To describe the AO-HDS, in my opinion, at least the following questions arose from experiments must be answered:

Is the AO-HDS caused by a huge effective magnetic field?

…”

Section: Questions Arose From Experimentsmentioning

confidence: 99%

Fundamental mechanism for all-optical helicity-dependent switching of magnetization

Chen

2017

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Switching magnetizations with femtosecond circularly polarized lasers may have revolutionary impacts on magnetic data storage and relevant applications. Achievements in ferrimagnetic and ferromagnetic materials of various structures strongly imply a general phenomenon of fundamental atom-laser interaction. Rotating an atom’s wave function with the rotating electric field of a circularly polarized laser, I show the quantum mechanics for the atom is equivalent to that in a static electric field of the same magnitude and a tremendous static magnetic field which interacts with the atom in somewhat different ways. When some conditions are satisfied, transitions of atoms in these two crossed effective fields lead to a highly nonequilibrium state with orbital magnetic moments inclining to the effective magnetic field. The switching finally completes after the pulse duration via relaxation.

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Manipulation of ferromagnets via the spin-selective optical Stark effect

Cited by 27 publications

References 42 publications

Ab InitioTheory of Coherent Laser-Induced Magnetization in Metals

Ab InitioTheory of Coherent Laser-Induced Magnetization in Metals

Light-induced spin polarizations in quantum rings

Fundamental mechanism for all-optical helicity-dependent switching of magnetization

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